1. Field of the Invention
The present invention relates to a network communication device having a plurality of removable circuit board units.
2. Description of Related Art
Switches and routers are widely known in a network field as network communication devices for transferring data. Generally, a network communication device like a switch or a router includes, for example, a circuit board unit having an interface function for data transfer in a network, a circuit board unit having a control function controlling the data transfer, and a circuit board unit having a crossbar switch function; and these circuit board units can be removed. Signals are exchanged between the respective circuit board units and electric power is supplied to each circuit board unit via a relay circuit board, that is, a back board, placed in the network communication device. Incidentally, the network communication device is generally mounted on a standard rack which is 19 inch wide.
Recently, the demand for enhancement of processing performance of the network communication device has been increasing and there is a high tendency to adopt an air flow structure of a front-back air supply and exhaust system in consideration of the environment where the relevant device is installed.
For example, an arithmetic processing unit that cools an arithmetic unit with intake air introduced through an intake hole in its front face, cools an input/output unit with the intake air introduced through a vent hole in the front face, gathers the intake air, which has passed through the arithmetic unit, and the intake air, which has passed through the input/output unit, and discharges it from its back side is disclosed as an example of a device which adopts the structure of the front-back air supply and exhaust system (see WO 2010/064299). Also, an electronic device designed as follows is disclosed: a plurality of circuit board units are placed in front of a relay main circuit board, and a cooling unit and a power supply unit are placed side by side on the back side of a relay sub-circuit board with the relay main circuit board placed between the plurality of circuit board units and the cooling unit and power supply unit. Intake air is introduced through a vent hole formed in the front side of each circuit board unit, the introduced intake air is introduced to the cooling unit via the relay circuit board and discharged from the cooling unit, the intake air is further introduced from a vent hole formed on both lateral sides of each circuit board unit, and the introduced intake air is discharged via the power supply unit (see Japanese Patent Application Laid-Open Publication No. 2011-146450).
Moreover, another application (WO 2012/0066732) discloses an electronic device designed so that a plurality of circuit board units are placed in front of a relay main circuit board, and a power supply unit and a cooling unit are placed in order on the back side of a relay sub-circuit board with the relay main circuit board placed between the plurality of circuit board units and the cooling unit and power supply unit. Intake air is introduced through a vent hole formed in the front side of each circuit board unit, and the introduced intake air is introduced via the relay circuit board to the power supply unit and then to the cooling unit and discharged from the cooling unit.
When adopting the structure of the front-back air supply and exhaust system, the following structure can be used: a first circuit board unit to be placed on a front side of a rack is mounted in the rack in a vertical direction, a second circuit board unit is mounted on a back side of the rack, a first cooling unit is placed in an upper part of the front side of the rack, a second cooling unit is placed on an upper side of the second circuit board unit, cooling air which has been introduced through a vent hole in a bottom of the front side of the rack, is introduced via the first circuit board unit to the first cooling unit and via the second circuit board unit to the second cooling unit, and each introduced cooling air is discharged from the first cooling unit or the second cooling unit.
In this case, the cooling unit is placed for each circuit board unit, so that each circuit board unit can be cooled sufficiently. However, if the first circuit board unit is mounted in the vertical direction in the rack, a limitation of the rack width will be imposed on the number of circuit board units to be added and, therefore, it becomes difficult to increase the number of the circuit board units. Particularly in a case of a network communication device, scalability to create devices with the increased or decreased number of the same circuit board units as a lineup will decrease. Also, two types of cooling units are required in order to sufficiently cool each circuit board unit.
On the other hand, it is possible to adopt a configuration to mount the first circuit board unit in a horizontal direction in the rack, place the second circuit board unit on the back side of the first circuit board unit, and place the cooling unit in the second circuit board unit. In this case, cooling air which has passed through each circuit board unit can be cooled by one type of cooling unit and then discharged. However, since the heat which has passed through the first circuit board unit enters the second circuit board unit, it is necessary to use a large-sized cooling unit in order to sufficiently cool the second circuit board unit.
On the other hand, in the case of the device described in the WO 2010/064299, the arithmetic unit is placed in the horizontal direction, thereby making it possible to enhance the scalability. Moreover, since the cooling air which has passed through the arithmetic unit and the cooling air which has passed through the input/output unit are respectively introduced into a fan box, the cooling air which has passed through the arithmetic unit and the input/output unit can be cooled by one type of a fan box.
However, with the structure of the device described in the WO 2010/064299, the cooling air introduced to the input/output unit is bent 180 degrees before being introduced to the fan box and then further bent 180 degrees, so that pressure loss of the cooling air increases. Furthermore, according to the structure of the device described in the WO 2010/064299, the arithmetic processing unit is the one placed on the front face of the rack and the input/output processing unit for inputting and outputting data to and from other devices is placed on the back face of the rack. On the other hand, in the case of the network communication device, a cable(s) connected to an external network is often connected to or disconnected from the font face of the rack for the purposes of construction, maintenance, and management of the network. Accordingly, a circuit board unit equipped with an external interface connector needs to be placed on the front face of the rack. Therefore, in consideration of the maintenance and management of the network communication device, it is necessary to place the circuit board units and the cooling units by adopting a completely different designing idea from that of the structure of the device of the WO 2010/064299.
On the other hand, in the case of the electronic device described in the JP Application Laid-Open Publication No. 2011-146450, the circuit board unit on the front side is placed in the horizontal direction, the cooling unit is placed on the back side, and the power supply units are placed on both sides of the cooling unit, so that the scalability of the circuit board units can be enhanced and the cooling air which has passed through each circuit board unit can be cooled by one type of a cooling unit and then discharged.
However, in the case of the electronic device described in the JP Application Laid-Open Publication No. 2011-146450, a plurality of relay circuit boards are required and the configuration becomes more complicated than that of an electronic device with one relay circuit board. Also, if a circuit board unit(s) which transfers data to other circuit board units, but does not directly communicate with external devices is placed on the front face, a circuit board unit equipped with an external interface connector cannot be placed and, therefore, the network cannot be extended flexibly. Moreover, with the electronic device that allows the circuit board unit, which does not communicate with external devices to be directly coupled to the circuit board unit equipped with the external interface connector in place of the relay circuit board, the circuit board unit located in the middle of a chassis cannot be cooled. Furthermore, with the electronic device described in the WO 2012/0066732, units such as the power supply unit on the back face of the chassis is cooled with the air taken in from the front face of the chassis and warmed by the circuit board unit placed at the front face of the chassis, so that cooling cannot be performed sufficiently.
The present invention was devised in light of the problems of the conventional art and it is an object of the invention to provide a network communication device capable of enhancing cooling efficiency with a simple configuration when adopting the structure of the front-back air supply and exhaust system.